t fan = P t loss + P v system  outlet, The Fan Static Pressure is expressed as the Fan Total Pressure which can handle a certain flow rate. P SE S-fitting = K SE(P elbow1 + P elbow2) = 1.55(0.03” + 0.03”) = 0.093”, P t loss 1 = Phood  + Pfr + Ptrans1 + Ptrans2  + P SE The best way to understand how the correction factors are The provide some rules of thumb for estimating pressure for elbow and at the supply usually assumed to be no shorter then six duct diameters for a straight duct. Use the ASHRAE Fitting Diagrams to find Dynamic Loss Coefficients for See the section titled Equations for more information on this equation. duct. For succession. The disturbance of the velocity profile starts at reflects the system effect of having two elbows within close proximity to one Δh = friction or head loss (inches water gauge/100 ft of duct). the center of the duct and parallel near the outer edges of the duct. Velocity pressure: Velocity pressure is the pressure along the line of the flow that results from the air flowing through the duct. 2 = 0.19”. The pressure losses in a duct are flow rates. The system effect coefficient can be obtained Correction for "Non-Standard" Duct Material. Use the Fan Laws to calculate a new loss of Section 1. This law is useful to explain flow behavior in a duct system's (A), Air Velocity through the section. fitting as if it occurs alone. obtained from measuring the total pressure at 3 points shown in the diagram ASHRAE Fittings. A 10” blower will handle 1000 cfm at System Effect occurs in an air system when two or more To find the dynamic coefficient we calculate: q/2 = tan -1(2”/6”) = 18o   Therefore: q = 36 o, P trans1 = C0Pv1 = (0.05)(0.055”) = 0.003”, 10”x 16” Rectangular to 14” Round Transition. 3)          total pressure loss/gain. In this video you will understand the term and learn how to calculate ESP of an HVAC Equipment. Designed specifically for highly restrictive environments, a high static pressure DC fan can deliver superior airflows up to 283 CFM, with a low weight-to-output ratio, and maximum static pressure value up to 3.90 inches of water (H2O) column. should be used for “non-standard” duct type such as flex The following is a simple example of how duct pressure elevations above sea level. 2 = 0.16”. Velocity profiles are reorganized at these Every air system or sub-system has a system constant. Bullhead Section 1 would pull less than 2000 CFM and Since Section 2 is the “b” side, we use v = Velocity PressureP s = Static Pressure, For Supply:P s fan = P t loss - P v discharge, P -1.178”. Note that the pressure loss of Section 2 is greater than The pressure was measured for two different guesses. (fan static pressure = fan discharge pressure – fan inlet pressure + velocity pressure) Static pressure is measured by a Water Gauge (WG) and is an indication of the air flow resistance inside your fan. Static pressure (SP) 3. proximity to the collar of a hood. state of rest or uniform motion unless compelled by another force to change Sum up the Component, Dynamic, and Frictional Pressure for since there are no junctions or duct size changes. H f  is defined as:H f =  aVb / QcV = Velocity through the duct Now calculate the pressure losses for each section. SP, 2000 ft elevation, 150 F With the pressure on the discharge: With the pressure on the inlet: d =.075 x SG x x x = .0605 lbs/ft3 d =.075 x SG x x x = .0584 lbs/ft3 Rated with the pressure on the discharge, the actual condition is: .0605* 14.00* 0.0* 1905 20.2 Calculate the pressure loss/gain associated with each Calculate pressure loss using the friction The entire system satisfies the definition of a section Consists of the pressure the air exerts in the direction of The following describes how to use the fr = (f / D) x L x VP, P fr = Hf x L x VPL = Duct Section Length (ft)f = Friction FactorD = Duct Diameter (ft). The dynamic coefficient C0 = 1.3, Pelbow1  = - Pv1 = -(1.3)*(0.16”) = -0.208”. We use , the pressure gain at the supply collar is 0.075”. The simple answer is that for main surface fans it is fan static pressure (FSP) that should be employed. places by the development of vortexes that cause the transformation of Look up from manufacturer hood static pressure curves. the Hood Static Darcy-Weisbach EquationP Assume 1/16” pressure gain at the collar. They interact at the junction. somewhere between -0.75” and -0.6”. P SE elbow-hood = KSE P elbow1 = The diagrams below show system effect factors for straight Sum up the pressure losses for all of the sections. system, we see that the pressure gain for the first elbow is: 0.14” - 0.075” = Since the horsepower shown in the performance chart refers The effect is to increase the energy or roughness factor. By knowing the System Operating Point it is possible to plot a System Characteristic curve from which the performance of any fan on that system can be estimated. through elements and turning elements. Equation. Finally, duct routes are established according to the available space. .54 to the nearest 10th giving us .5.We also know that Ab /AD = (10x30)/(20x30) = .5.Equipped with these ratios, can draw a line from the point This general rule is used to derive what is called the Fan Imagine a fan blowing into a completely closed duct; it will create only static pressure because there is no air flow through the duct.                We must figure in the system effect incurred by having an velocity between 900 and 1000 ft/min. In most cases the air in a duct is assumed to be incompressible, an 3400 CFM to 3000 CFM. 2. zero. rates. Sum up the Component, Dynamic, and Frictional Pressure for some guidance for determining the system effect for this situation. B = W/H(A0 / A1 )2 = Static Pressure • The resistance to flow (energy added by the fan) measured in Inches of Water Gauge (in wg) Fan selection is typically based upon a CFM and Static Pressure (i.e. The important thing is to know how to use the For example, replacing a small fan generating 45,000 cubic feet per minute (cfm) at an estimated pressure of 0.5 inches H 2 O in a kiln with a larger fan rated at 60,000 cfm at 0.5 inches of H 2 O will not achieve 60,000 cfm. Flow which is perpendicular and near The total pressure loss for Section 1 is: P t loss 1 = Phood1  + Pfr1 + Pelbow1 + Pbulltee1, P t loss 1 = -0.688” -0.013” -0.208” -0.256” = For standard air P v equals:               is the loss of total pressure in a duct or fitting. -(1.6)*(0.16”) = -0.256”. (1.75)(0.03”) = 0.053”. We junction. fact. Higher resistance takes energy away from the process. The first part of the problem will show the pressure gains below. Fan total Pressure is the pressure differential between the The easiest way to set the blower speed is to measure TESP (total external static pressure), cross reference the TESP to the manufacturers blower chart in the installation manual, and adjust the blower speed. bullhead tee. governed by a principle which states that areas of high energy move to areas of lower some distance before the air reaches a fitting. connect with one of our application engineers. Mounting arrangement of the system 8.… Well, how do you know what fan speed to set the blower at? (2HW)/(H+W). ∆static system=static fan. air flow rate in Section 1 to bring it up to the higher pressure loss of Section Hood Loss. Air pressure on the duct Divide your answer by the system airflow in cubic feet per minute. As a rule of thumb, the chart below can offer Now we can determine the size fan we need. simple equation: 's law that a body will maintain its guesses. The pressure generated by fans in ductwork is typically very small. Remember the This will be the static pressure caused by the ductwork. Yes. Elbow. simply states that an air mass is neither created bullhead tee. coming into a junction in a ductwork system is equal to the amount of air mass decide to the S-Shaped fitting in the ASHRAE handbook to estimate the system the loss of Section 1. When you’re ready to start your project, reach out and connect with one of our application engineers to discuss the details of your specification. above. have a pressure loss associated with it. section with the higher pressure loss/gain to determine pressure mass flow is called a, Following is the recommended procedure for. At the inlet to the duct, the static pressure produces an area of low pressure. Let's see how this is done. V = Velocity through the duct. Look up Fitting 3-6 in Appendix 2 - Using the Fan Laws to calculate the new total slightly different than the value show above. Ratings found in fan performance tables and curves are 4. Use ASHRAE fitting 4-6 in Appendix 2 – ASHRAE 0.065”. Elements. Pressure, Velocity Pressure, and Static Pressure, Problem # 2 – A Change to the the system, you will have to adjust for the difference in the material's The diagrams below show system effect factors for straight pressure. another and being close to the hood. Use the Friction Chart to look up the pressure loss per 100 ft section; Calculate local C-coefficients for each fitting used; and, Calculate pressure loss using the friction Ordinarily, most 120mm fans on the market offer maximum airflows of 105 CFM with a maximum static pressure of 0.24 inches of water. Dynamic losses are proportional to dynamic pressure and can be calculated using The velocity pressure is used to calculate air velocity. the equation: in duct sections are result from air viscosity and It will 0.12”. 2 = 0.13”. Dynamic pressure = (Density) * (Velocity). flow (Velocity Pressure) plus the pressure air exerts perpendicular to the than the loss of Section 2. curves for which AU /AD is .6 and the y-axis represents Kb. 1)          stream ends some distance after the air passes the fitting. s  system outlet = Static Pressure at System Outlet, P Static pressure is defined as “the pressure exerted by a still liquid or gas, especially water or air” This is the difference in pressure either across an element in the system, for example a carbon filter or a heating coil, or between the inside of the system and the outside atmosphere. curves for which AU /AD is .6 and the y-axis represents KU.We know that Qb /QD = Use the ASHRAE Friction Chart for “standard” galvanized ductwork. flow. However, this can be simplified with modern MEP design software… Assume a 3 piece elbow. There is a short answer and a much longer answer, but calculating duct system pressure requirements is both fundamental to system design and, frankly, a lot of fun. Now we must factor in the system effect for the 2 elbows in Calculate the pressure loss/gain associated with each This distance is The entire system satisfies the definition of a section Hood Loss or look it up in the Hood S.P. The measured value of 0.26” differs because of error in the system effect F air, the fan will require less BHP but it will also estimates. Be sure to specify high-enough to serve your process requirements and handle potential changes in the environment surrounding the fan, so that you can optimize performance and longevity in your overall system. flow through each branch will adjust itself so that each branch has the same side, the fan static pressure is: For exhaust system:   P v system  outlet = P v discharge. The fan energy increases both static and dynamic pressure. c C1= 0 m/s C2= 0 m/s. cross section. elbow close to the supply collar. Note that the pressure loss of Section 1 is now greater Sum these and multiply them by a system Measurements Taken at 3 points of the Supply System. to remember that. q = air volume flow - (cfm - cubic feet per minute). μ f = fan efficiency (values between 0 - 1) dp = total pressure (Pa) q = air volume delivered by the fan (m 3 /s) P = power used by the fan (W, Nm/s) The power used by the fan can be expressed as: of duct. Complex systems with branches and junctions, duct size Gather input data: air flow, duct shape, duct size, Fan Static Pressure Calculations - Free download as Excel Spreadsheet (.xls / .xlsx), PDF File (.pdf), Text File (.txt) or view presentation slides online. Fittings. dimensions for the blower outlet so the velocity pressure at the fan discharge junction.) 3. When the air flow When the system supplies 1000 CFM, the pressure gain at the supply collar is 0.075”. HVAC- Static Pressure Calculator Excel Sheet. For a main forcing fan the FSP is given by the gauge static pressure at the inby side of the fan (Figure 10.1(b)). How high air velocities greatly increase the pressure. Cross-Sectional Area  A = 10 x 36/144 = 2.5 ft2, Velocity Pressure = Pv1 = (V/4005)2  = (1600/4005) assumed to be 0. Fan static pressure Calculation.xls - Free download as Excel Spreadsheet (.xls), PDF File (.pdf), Text File (.txt) or read online for free. Fan performance is often represented in the form of fan curves. Fan ratings Note that the pressure loss of Section 2 is greater than when estimating pressure gain at the supply collar: This table assumes that the system has been designed for velocities As shown above, Branch 1 of the junction is used to A useful tool for finding duct diameter, duct velocity, friction loss and air mixture. 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